VENTILATION. BY HENRY B. BAKER, M. D., SECRETARY OF STATE BOARD OF HEALTH, LANSING, MICH. [ Reprinted from the Annual Report of the Michigan State Board of Health for the fiscal year 1894.] [ Reprint No. 459.] Mr. President, Ladies and Gentlemen: *In the time allotted to me, I propose to suggest some of the general facts and principles which need to be understood by all who have to do with the subject of ventilation. These general facts and principles may be profitably studied in groups, as follows: 1. Facts relating to the constant needs of the living body for unbreathed air. 2. Faots relating to air and its movements with reference to the parti¬ cles whioh constitute the specific causes of diseases. 3. Faots relating to the oauses of movements, and the rates of move¬ ment of air. Quantity of Air Needed for Respiration. 1. In the first-mentioned group is the well-known faot that unless fresh air is supplied to the human body, life is not sustained. Fresh air is needed to supply the body with oxygen which is consumed in the vital processes whioh yield the forces and motions which constitute the phe¬ nomena of life. Fresh air is needed also to displace, drive away, and remove produots of vital aotion, which, if allowed to remain in the body, poison it and lead toward death. How much fresh air is needed? Those who have studied this subject have generally agreed that about 2,000 cubio feet of fresh air per hour is a fair allowance for each person; and as the vital processes of children are more rapid than those of adults, I believe that school children should have as much as adults. There is a common fallacy that in a large room a less quantity of air per hour is sufficient. That is true only for the very short time until the air of the room has been once used. However, the ruom should be large enough to allow at least twenty-five square feet of floor space to each pupil or person; and high enough to allow at least six hundred oubio feet of air space to each pupil or person. One reason for this is that in a less spaoe per person the requisite quantity of air cannot be moved through the spaoe without causing drafts which are dangerous to health. Just how drafts cause sickness may not be fully dealt with here and now; but that drafts do oause sickness has been abundantly proved. In order to prevent drafts the space allowed for each occupant of a room must not be less than as just stated. ♦This was a paper read at the Sanitary Convention held at Hillsdale in July, 1893. cxxx STATE BOARD OF HEALTH.—REPORT OF SECRETARY, 1894. Proper Location of Foul-air Outlets. 2. Kecent progress in sanitary soience has demonstrated the fact that many diseases, now known as “speoific, ” are caused by living organisms, microsoopic in size, but particulate, having weight, being capable of set¬ tling as dust upon floors and artioles in inhabited rooms. In the human body, there seem to be many natural protections against the inhaling of such dangerous particles. In the first place the normal nose is so formed as greatly to avoid catching dust particles which being heavier than air have a downward motion—the normal nostrils do not open upward, they open downward. In the next place, the opening of such nostril is generally protected by fine hairs, which, being moistened by the air exhaled, tend to catch and prevent the entrance of dust. Thirdly, normal secretions of the membranes of the nose and throat tend to stop the further entrance of particles; and the nasal mucus has power to destroy at least some of the germs of disease. Notwithstanding these protections, disease germs do gain entrance into the body under favoring conditions. A proper system of ventilation must take account of this group of facts, and must ensure that the general movement of the air of every inhabited room shall be downward. This makes it essential that the foul-air outlet of every room should be at the floor level. And it is best that the fresh-air inlet shall not be in the floor. It is not well either, as a rule, that the external source of fresh air shall be at the ground level, because of the liability to take in injurious dust. Causes of Movement of Air , and Pates. 3. In cne third group the most important fact, with reference to natural ventilation, is this—that, except as caused by fans, blowers, and other mechanical means, movements of air result from differences in weight of air at different temperatures, warm air being expanded air, and therefore lighter than cold air, which is denser,—in other words, heavier. Accordingly, warm air rises when its place is supplied by colder air; and cold air tends to fall in under and to displace warmer air. The rate of this movement of air depends upon the amount of the difference in the tem¬ peratures of the two bodies of air, and upon the height of the two oolumns of air—the displaced and the displacing oolumns of air. I have here a table, taken from Parkes’ Hygiene, stating the rate of movement of air under different conditions of temperature and height of column. I will not undertake to read the entire table, but will merely state a few of the conditions and resulting rates of movements. VENTILATION. cxxxi Table to show the Velocity of Air in linear feet per minute. Calculated from Mont¬ golfier's formula; the expansion of air being taken as 0.002 for each degree Fahren¬ heit , and one-fourth being deducted for friction. (Round numbers have been taken.) Difference Between Internal and External Temperature, stated in degrees Fah., 3 to 30 degrees. Helgb colum feet. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 30 10 88 102 114 125 135 144 153 161 169 176 188 190 197 204 210 216 222 228 283 239 244 249 254 279 11 92 107 119 131 141 151 160 169 177 185 192 200 207 213 220 226 233 239 245 250 256 261 267 292 12 96 111 125 136 147 158 167 176 185 193 201 209 216 223 280 237 248 249 255 261 267 273 279 305 13 100 116 130 140 153 164 174 183 192 201 209 217 225 232 239 246 253 259 266 272 278 284 290 318 14 104 120 135 147 159 170 181 190 200 209 217 225 233 241 248 255 262 269 276 282 289 295 301 330 15 108 125 189 153 165 176 187 197 207 216 225 283 241 249 257 264 272 279 286 292 299 305 312 341 16 111 120 144 158 170 182 198 204 213 223 232 241 249 257 265 273 281 288 295 302 309 315 322 353 17 115 133 148 162 176 188 199 210 220 230 239 248 257 265 274 282 289 297 304 311 318 325 832 363 18 118 186 153 167 181 193 205 216 226 237 246 255 264 273 282 290 298 305 813 320 827 335 342 874 10 121 140 157 172 186 198 210 222 233 248 253 262 272 281 289 298 306 314 321 329 336 344 351 884 20 125 144 161 176 190 204 216 228 239 249 259 269 279 288 297 805 314 322 330 838 345 853 360 394 21 128 147 165 181 19? 209 221 233 245 255 266 276 286 295 304 313 321 330 338 346 354 361 369 404 22 131 151 169 185 200 214 226 239 250 261 272 282 292 302 311 320 329 338 346 354 362 370 378 414 28 134 154 173 189 204 218 232 244 256 267 278 289 299 309 318 327 336 345 354 362 370 378 386 423 24 136 158 176 193 209 223 237 249 261 273 284 295 305 815 325 835 344 853 361 370 878 886 394 432 25 189 161 180 197 213 227 241 254 267 279 290 801 312 322 832 342 351 860 369 378 886 394 402 441 26 142 164 183 201 217 232 246 259 272 284 296 307 318 328 338 348 358 867 376 385 394 402 410 450 27 145 167 187 205 221 237 251 264 277 290 302 313 324 335 845 355 365 374 383 392 401 410 418 458 28 147 170 190 207 225 241 255 269 282 295 307 319 330 341 351 361 371 381 390 899 408 417 426 467 29 150 173 194 212 229 245 260 274 287 800 312 324 335 347 357 368 378 388 897 407 416 425 433 475 30 153 176 197 216 233 249 264 279 292 305 318 330 341 353 363 874 384 394 404 414 423 432 441 483 31 155 179 200 219 287 253 269 283 297 310 823 335 347 358 3«9 380 391 401 411 420 480 439 448 491 32 158 182 204 223 241 257 278 288 302 315 328 341 358 364 875 386 . : 97 407 417 427 437 446 455 499 33 160 185 207 226 245 261 277 292 307 320 338 346 358 870 881 392 403 414 424 434 443 453 462 506 34 162 188 210 230 248 265 282 297 311 325 338 351 863 375 887 398 409 420 430 440 450 460 469 514 35 165 190 218 233 252 269 286 301 316 830 343 856 369 381 893 404 415 426 436 447 457 467 476 522 86 167 193 216 236 255 273 290 305 320 384 348 361 374 386 398 410 421 432 442 453 463 473 483 529 87 170 196 219 240 259 277 294 310 325 339 353 366 379 392 404 415 427 438 44S 459 470 480 490 536 38 172 198 222 243 262 281 298 314 329 344 358 871 384 397 409 421 432 444 454 465 476 486 496 543 39 174 201 225 246 266 284 302 818 833 348 362 376 889 402 414 426 438 450 461 471 482 492 503 551 40 176 204 228 249 269 288 305 322 338 353 867 381 394 407 420 432 444 455 467 477 488 499 509 558 45 187 216 241 264 286 305 324 341 858 374 889 404 418 432 445 458 471 483 495 506 518 529 540 591 50 197 228 254 279 301 822 341 360 377 394 401 426 441 455 469 483 496 509 522 534 546 558 589 623 De¬ grees Fahr. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 80 This table is taken from Parkes’ Hygiene, American Edition 1884, William Wood and Co., page 194. Its reading is easy, but may be illus¬ trated as follows: Suppose the height of the shaft is 10 feet, and the difference in temperature outdoors and indoors is 3 degrees (as in the first line, first two columns) then the rate of movement of the air is 88 linear feet per minute. Suppose the height of the shaft is 14 feet, and the difference in temperature is 11 degrees; then the velocity of the air is 200 linear feet per minute. If thirty persons in the room are eaoh to have 2,000 cubic feet of air per hour, all are to have 1,000 cubic feet per min¬ ute, then, under the conditions named, the cross-section of the shaft must have an area of five square feet. In praotioe, however, it is seldom that a foul-air shaft is not higher than 14 feet. The foregoing rates are in ordinary straight shafts with no extra oause of friotion; if the shafts are very small, or the friction unusual, the rate of movement is lessened. cxxxii STATE BOARD OF HEALTH.—REPORT OF SECRETARY, 1894 It is a general fact,that must be held in mind, that eaoh right angle in a shaft reduces the velooity of the air in that shaft one-half. Given the number of proposed inmates of a room, the height of the shaft, and the difference of temperature between the in-door and the out¬ door air, then the sizes of inlets, outlets, and shafts, can be computed, by means of the data which have now been stated, allowing two thousand cubic feet of air per hour per person. In this climate there is no difficulty in securing good ventilation in the warmest weather, because then windows and doors are usually open; nor in the coldest weather, beoause then the difference in temperature is so great between the out-door and the in-door air that very rapid movement of the in-door air is caused by permitting to be balanced against it a col¬ umn of dense out door air. The difficulty in securing ventilation occurs in the spring and autumn, when there is little difference in the tempera¬ ture of the in-door and the out-door air. The ventilation of every inhab¬ ited room should be so planned as to be susceptible of regulation and especially of extension or expansion, by means of registers into flues and shafts of a size ample for times of slight difference in temperature of the out door and the in-door air. The calculations for sizes of inlets, outlets, flues and shafts, should be made upon the basis of a very slight difference of temperature. Each Boom Should Have Separate Ventilation. One important principle which is perhaps most frequently violated by architects, contractors, and builders, was stated by Prof. R. C. Kedzie in the first Annual Report of the Michigan State Board of Health, page 95, as follows: “For successful ventilation I oonsider it essential that the foul air of each room shall enter a separate compartment in the ventila- ing shaft, and not one common shaft.” The old “Ruttan” system, and the “Smead dry-closet system” both violate this very important principle. Some of the reasons why it is important that the foul-air shaft from each room shall extend separate and distinct to the outer-air, are as follows: It is praotically impossible to so control all the conditions that the pres¬ sure of air into two rooms shall always be the same; all openings into one room (except registers) may at some time be closed, while at the same time a window or a door into the other room may be open; one room may be on the side toward whioh the wind is blowing, while the other room is on the side from which the wind is blowing; in such cases a oommon vent shaft is filled with air from the room into whioh the pressure of air is greatest, to the exclusion of the foul air from the other room, whioh is, therefore, not ventilated. An instance, at one of the State asylums in Michigan, will illustrate another reason: foul-air shafts from rooms on both sides of the building extended up to the* attic, where they terminated in that common reoeptaole from which a oommon shaft extended through the roof. During a wind, a window being open in a room on that side of the building on whioh the wind did not blow, a current of foul air was found to come down from the attic through the foul-air shaft and go out of the window, there being a constant circulation of foul air through the room, while the warm fresh air which was supposed to enter the room through a transom was not entering; the only air supplied to the inmate of the room being the foul air from the other side of the building, which VENTILATION. CXXXlll might be not only impure with produots of respiration, but also oontain the germs of any oommunioable disease which like consumption might be present in the other rooms of the asylum. Such “baok-drafts” are not unoommon in school buildings in which this principle under discussion is violated; and suoh “back-drafts” are believed to be especially danger¬ ous where they oome from excreta which is dry from which germs of disease may then be detached and float in the foul air. In the discussion following a paper by Prof. French of Hillsdale and this paper, Dr. Baker said:—I do not believe in having the heat from steam pipes in the rooms; I think it is a vicious system. If we are to have the heating by steam, whioh I agree with the Professor is the pleas¬ antest, perhaps, unless it is the hot water, the steam pipes should not be in the room, but should be where the fresh air, in coming from out of doors, shall pass over them into the room; that is called the “indirect” system. The method of heating by steam, having the coils in the room, is a vicious system, and there is no good way of ventilating in such a way of heating. You can smell the results of it as soon as you enter the room ; the exhalations when the pipes are cold are oondensed on the pipes, when they are heated again, they give them off; but the main difficulty is that, in that method of heating, there is no provision for fresh air. The “direct” method of steam heating is vicious, and ought not to be employed, as a rule, anywhere. The steam ooils should be outside of the room, and the fresh air should pass over those coils into the room, and then, in the proper system, the air at the floor level is carried off. Prof. Delos Fall , Albion .—With the direot system of heating, by steam, the system of ventilation is an extra affair, and must be worked out by itself; you have to provide an extra plaoe for your air to oome in and go out. You can provide that, of oourse, you can have a plaoe for the fresh air to come in from outside of the building, and you oan have a place for it to go out at the floor level, with the ooils in the room; but the air comes into the room oold when its draft is often dangerous, and I see no way of having a proper supply of fresh air in the “direot” method of steam heating. Mr. Goodrich , Hillsdale —I would like to ask if there is much differ¬ ence, as far as the heating and ventilation is concerned, between the steam heat and the hot water system? Dr. Baker , Lansing —In the coldest weather, there is perhaps an advantage in having the steam; but there is a disadvantage in the spring and fall, when one needs a little heat, and not very much. If you have to heat the pipes up to 212 degrees before you get any heat, and then all at onoe you get great heat, that is not a very pleasant way to do. If you have the “indireot” method of heating, by means of hot water, you have the ideal system. It is expensive, perhaps; but when the fire is built and the water in the boiler is heated a few degrees, the circulation com¬ mences, and the incoming air is warmed, little or much as you desire; that is the great advantage of heating by hot water, that the heat is more easily suited to the temperature of the air in the spring and autumn months. In the coldest weather, it is an advantage to have the hot-water cxxxiv STATE BOARD OF HEALTH.—REPORT OF SECRETARY, 1894. % surfaoe line in the boiler below the level of the radiator, and so heat by steam; that is a method that is easily accomplished by simply lower¬ ing the water in the boiler; and instead of passing the water through the coils, pass steam through; that can be done in the cold weather, and in the spring or fall the hot water can be used. 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